Each of CD-DA (Compact Disc Digital Audio) and dts-CD (Digital Theater System Compact Disc) is specifications which define a music file recorded in a CD recording medium. CD-DA has a feature that sound quality does not degrade by virtue of digital sound recording of a piece of music using a PCM (Pulse Code Modulation) method having a sampling frequency of 44.1 kHz and 16-bit quantization. In contrast, a dts-CD is a medium recorded according to the dts-CD format specifications, and cannot be played back via an analog output of a general CD player, but can be used to reproduce a high-quality signal of 5.1 channels via a digital output using a decoder for DTS.
Recently, users have become able to acquire music files transmitted through network electric delivery by downloading them, and have mixedly recorded these music files which may have different data formats into a single disc frequently to listen to them.
By the way, data which comply with each of above-mentioned CD-DA and dts-CD specifications are recorded into a CD recording medium, and it is difficult for any playback equipment to identify whether a CD recording medium is a CD-DA medium or a dts-CD medium without analyzing actual data recorded in the CD recording medium. A conventional playback apparatus inputs data recorded in a disc to a decoder and discriminates whether the disc is of CD-DA type or dts-CD type from a response of the decoder.
However, because this method requires much time before the media type is determined and an audio is then outputted, there is a case in which the user doubts that the CD medium is a defective or the playback apparatus is out of order. A further problem with the conventional playback apparatus is that even if the conventional playback apparatus judges that the disc is of dts-CD type when discriminating whether the disc is of CD-DA type or dts-CD type from the response of the decoder, the conventional playback apparatus cannot output the audio correctly when data yet to be played back, except the data inputted to the decoder, are based on the CD-DA specifications. Furthermore, the same problem arises in playback of data having the same extension.
Conventionally, a playback apparatus that detects a stream synchronizing signal immediately before inputting data read from a CD to a decoder in order to judge whether a digital acoustic signal recorded in the CD is a PCM digital acoustic signal or a stream signal compression-coded at a variable-length bit rate, such as a signal based on MP3 (MPEG Audio Layer level 3), is known (for example, refer to patent reference 1). The conventional playback equipment judges the type of the data by detecting the stream synchronizing signal, and counts the amount of data so as to determine the next-time address. When the counter reaches a predetermined value, the conventional playback apparatus judges that the digital acoustic signal is a stream signal, whereas when the counter does not reach the predetermined value, the conventional playback equipment restarts the detection of the synchronizing signal from an address leading the determined address.    [Patent reference 1] JP, 2005-259220, A
However, according to the technology disclosed by above-mentioned patent reference 1, while it can be judged whether or not the digital acoustic signal is a stream signal before the digital acoustic signal is decoded, it is necessary to count the amount of data regardless of whether the counter reaches the predetermined amount. Furthermore, because the conventional playback apparatus has to carryout the detection of the synchronizing signal again when the counter does not reach the predetermined amount, the conventional playback apparatus requires useless time until it outputs an audio and therefore does not prevent a bad influence from being exerted on the playback starting time. Thus, the technology does not provide any solution to the case in which the user doubts that the CD medium is a defective or the playback apparatus is out of order.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a disc playback apparatus that shortens the playback starting time so as to prevent the user from doubting that the disc playback apparatus is out of order.